Surprisingly, no. The platforms can't move fast or else the portal will tip over, or they would have to be invincible turrets. It could be achieved through some clever use of triggers.

Ehm, I haven't been in portal's sdk in awhile, (more of a tf2 mapper) but couldn't you just parent the turret to the platform?
Then with input/outputs, and perhaps some nodraw physboxes around the turret, you could make it so it's parent is cleared if it's touched.